Tachometer LM2917

Discussion in 'General Electronics Chat' started by Limoez, Aug 6, 2014.

  1. Limoez

    Thread Starter New Member

    Jul 30, 2014
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    0
    Hello,

    I have been looking at all of the threads that deal with the LM2917 tachometer trying to find a solution. I am building an engine monitor for a rotary engine in an aircraft. I am using an arduino and want to feed the voltage from the LM2917 to the arduino. I built up a test setup that spins the CAS sensor to RPMs and measuring the rpm with a photo tach. I have tried various resistors and caps but I am getting a steady increase in voltage to about 3000 rpm then the voltage goes down. I am putting redline at 4500 rpm. Does the input voltage amplitude affect the output? Is the input voltage so high from a VR sensor that it is causing this?

    I have another circuit that uses a LM1815 that cleans up the wave form and limits it to 5 volt output. It does not work when connected to the LM2017. I suspect that it is not going negative only to 0. How do I adjust the input to go negative? I am using the LM2917 circuit in the data sheet for the 14 pin chip. The LM2917 circuit uses 12 volts while the LM1815 uses 5volts. I am using a regulated supply. Appreciate any help. Thanks

    Joe Berki
     
  2. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,571
    2,381
    Have you considered using the tach signal direct without the use of LM2917?
    I am not sure of the capabilities of the Arduino, but I have done this fairly easily with a PICmicro.
    Max.
     
  3. Limoez

    Thread Starter New Member

    Jul 30, 2014
    3
    0
    I do not want to use interrupts as there are a lot of inputs
     
  4. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    You don't need interrupts, just use the tach pulse signal to operate the timer in the micro.
     
  5. Limoez

    Thread Starter New Member

    Jul 30, 2014
    3
    0
    Could you steer me to examples in arduino to operate timers?
     
  6. THE_RB

    AAC Fanatic!

    Feb 11, 2008
    5,435
    1,305
    Sorry I'm not an Arduino user. But there should be a ton of examples on the net if you do a quick google. :)
     
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